Mineable oil sands, also known as tar sands, typically contain mixtures of oil, sand, clay, and water. These sands can be mined, and the oil (which may also be referred to as bitumen) component removed for further processing or use. The composition of oil sands can vary considerably from location to location, hence, the preferred method used to remove the bitumen from the sand and clay can tend to change considerably as well between different locations. In many instances, bitumen is separated from the mined sand and clay by mixing the components with a liquid, such as water or an organic liquid.
A typical organic liquid solvent extraction process is described, for instance, in “A Solvent Extraction Process for Oil sand”, R. J. Graham, et al. This reference describes the manner in which ore from an open pit mine is initially crushed in mills. To achieve extraction, bitumen is dissolved in heptane solvent, and the coarse sand is separated from the solvent/bitumen. The fine mineral is removed by pentane deasphaltening in the course of fines removal, and solvent is recovered from the coarse tailings by steam stripping. After the solvent has been recovered from the bitumen, the bitumen may be topped in a crude unit. The process can produce both coarse filings, which are disposed of, and fine tailings, which are ultimately recovered and conveyed to a circulating fluid bed combustor.
By comparison, in a conventional water based process, the bitumen is first, and largely, removed in the form of a bitumen “froth” by mixing the extracted oil sands with hot water. The bitumen can gravity separate from the clay and sand, resulting in a bitumen-rich phase, a solid phase, and an intermediate phase of clay and/or sand suspended in water. The solids phase and the intermediate suspension can, alone or in combination, be referred to as oil sand tailings or, at times, effluent. Further separation of the water from the clay and/or sand in the intermediate suspension can be difficult because the suspension may include extremely fine particles of clay that form a stable suspension. Currently, suspensions of this type are being accumulated with no immediate disposition.
Increased attention is being paid to oil sands, including for instance, a directive issued by the Energy Resources Conservation Board (ERCB) of Alberta, Canada, which will be applied to the reclamation practices at all mineable oil sands operations within their jurisdiction, and which will require the reduction of fluid tailings and their conversion into trafficable deposits. See “Tailings Performance Criteria and Requirements for Oil Sands Mining Schemes” directive issued by The Energy Resources Conservation Board of Alberta (ERCB/Board) on Feb. 3, 2009 (“Directive 74”). This directive sets out new requirements for the regulation of tailings operations associated with mineable oil sands, and is particularly concerned with the conversion of fine tailings extracted from oil sands into trafficable deposits (i.e., deposits that can support traffic).